Interactomes can be used to define the interactions between an enormous number of constituent proteins, and thus the interactome of the model plant Arabidopsis should reveal fundamental insight into plant biology (see the Perspective by Landry). The Arabidopsis Interactome Mapping Consortium describes the generation and analysis of a proteome-scale, binary protein-protein interactome map of Arabidopsis. With this resource, Mukhtar et al. investigated hundreds of proteins implicated in immune system function and their interactions with proteins from two evolutionarily disparate pathogens. A “plant-pathogen interaction network” revealed interactions between pathogen effectors and plant proteins and suggests that divergent pathogens attack a highly overlapping set of host proteins that interact with a common set of plant immune system receptors.